This is a fairly old story but this Guardian story sheds some new light on it by including info from recently declassified documents. Here's a little bit from the story at Guardian Unlimited Special reports How Bush's grandfather helped Hitler's rise to power:

"His business dealings, which continued until his company's assets were seized in 1942 under the Trading with the Enemy Act, has led more than 60 years later to a civil action for damages being brought in Germany against the Bush family by two former slave labourers at Auschwitz and to a hum of pre-election controversy.

The evidence has also prompted one former US Nazi war crimes prosecutor to argue that the late senator's action should have been grounds for prosecution for giving aid and comfort to the enemy.

The debate over Prescott Bush's behaviour has been bubbling under the surface for some time. There has been a steady internet chatter about the "Bush/Nazi" connection, much of it inaccurate and unfair. But the new documents, many of which were only declassified last year, show that even after America had entered the war and when there was already significant information about the Nazis' plans and policies, he worked for and profited from companies closely involved with the very German businesses that financed Hitler's rise to power. It has also been suggested that the money he made from these dealings helped to establish the Bush family fortune and set up its political dynasty."

AmericaBlog also has this comment: "That's right. Bush is being sued by survivors of Auschwitz (!)because they say his family profited from the death camps. The Guardian also suggests that one reason Bush backtracked on Clinton's support of the World Court was because his family could be dragged in front of it!"